Explanation: Welcome to the December solstice, a day the world does not end … even according to the Mayan Calendar. To celebrate, consider this dramatic picture of Orion rising over El Castillo, the central pyramid at Chichén Itzá, one of the great Mayan centers on the Yucatán peninsula. Also known as the Temple of Kukulkan it stands 30 meters tall and 55 meters wide at the base. Built up as a series of square terraces by the pre-Columbian civilization between the 9th and 12th century, the structure can be used as a calendar and is noted for astronomical alignments. In fact, the Mayans were accomplished astronomers and mathematicians, accurately using the cyclic motions of the stars, Sun, Moon, and planets to measure time and construct calendars. Peering through clouds in this night skyscape, stars in the modern constellation Orion the Hunter represented a turtle in the Mayan sky. Tak sáamal.

Astronomy Picture of the Day

Explanation: This sharp telescopic field of view holds two bright galaxies. Barred spiral NGC 5101 (top right) and nearly edge-on system NGC 5078 are separated on the sky by about 0.5 degrees or about the apparent width of a full moon. Found within the boundaries of the serpentine constellation Hydra, both are estimated to be around 90 million light-years away and similar in size to our own large Milky Way galaxy. In fact, if they both lie at the same distance their projected separation would be only 800,000 light-years or so. That's easily less than half the distance between the Milky Way and the Andromeda Galaxy. NGC 5078 is interacting with a smaller companion galaxy, cataloged as IC 879, seen just left of the larger galaxy's bright core. Even more distant background galaxies are scattered around the colorful field. Some are even visible right through the face-on disk of NGC 5101. But the prominent spiky stars are in the foreground, well within our own Milky Way.